Micah Toll’s DIY battery pack building kit

Normally, we are skeptical of kickstarters, and we usually hold off on judgement until they are over. This is so we can see if the owner actually comes through with the product that they promised, and also see if the quality and performance of the products are just as good as they claimed it would be.

However, this time?…we know this guy, and he is the real deal. Not only that, he is the first to provide a product that is sorely needed in the ebike world, and this effort is well-designed. And…Micah Toll has been doing this for quite a while, so this is not his first rodeo.

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So, who is this guy?

Micah Toll was an engineering student at Pitt University in Pittsburgh, Pennsylvania. In July of 2013, he had a successful Kickstarter to get a book off the ground, which spells out how to select components to add an electric bike kit to a bicycle. This book continues to be a useful reference for anyone who is new to ebikes, and wants to have all of the information you need to get started, all in one place.

I’m only listing his background so you will understand that Micah is not new to ebikes or their battery packs. Also, he has already paid his dues by providing a lot of free resources on the internet, to supply information to anyone who might need it. He is a true enthusiast who has been building and riding electric bikes for many years.

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Back to the modular pack-building kit

You may be wondering why he chose a modular battery pack building kit as his next effort.

About three years ago, high-performance 18650 cells that could put out a lot of current became available in the form of professionally-built battery packs for ebikes. Before that, the only way to get authentic (non-counterfeit) high-current name-brand cells, was to buy a lot of cordless tool battery packs and cut the cells out. Here is a discussion thread from 2011 to show what I mean.

Next, adventurous pack-builders had to decide how to configure the pack, and then to connect all the cells. If you want to be able to plug in the pack to a BMS, or to a balancing RC charger, you needed to build up groups of paralleled cells first, and once you had those parallel modules made, you could connect them in series to achieve the desired voltage. The key point to remember for later on in this article is that you first have to make up the paralleled sub-groups.

Here’s an example of one of the kit options, and what the result would be when the pack is done.

When you are connecting a lot of cells in parallel, and also then in series, many builders used thick pieces of copper wire, and soldered them onto the cell-ends. This is how we discovered that…in spite of our best efforts, occasionally one of the cells would become damaged from the heat of the soldering iron.

Soldering braided copper wire directly onto the cell-ends to form the the 6P parallel groups, for a 10S pack (36V).

As you can imagine, it is a huge headache to find the one bad cell in the middle of a pack, and then swap-out a new cell in its place. In order to avoid damaging any cells with a certain amount of confidence, some pack builders began buying spot-welders, which is the method that professional factories use. These spot-welders have come down in price, but they are still a major purchase, especially if you only need one battery pack. (plus most of them use 220V)

There have been several youtubes and articles showing how to spot-weld a pack together, and this has blossomed a renaissance of garage pack-building. This is important for two reasons. First, it remains very difficult to ship lithium 18650 cell battery packs into certain countries, even though it is fairly easy to ship in loose individual cells, and also the spot-welders.

[Here is an article with an embedded video showing the entire process of spot-welding the entire pack, to see what that entails]

Secondly, Even in countries where professionally-built battery packs can be shipped to ebike customers, it is becoming increasingly difficult to do that, and also more expensive each year.

That being said, the magic number to remember right now is that battery packs that are 100 Watt Hours (WH) or less are considered reasonably safe (this allows passengers to carry a laptop or smart phone with a lithium battery inside it, while still limiting very large packs). To determine the WH, you multiply the nominal volts times the Amp-hours. The Panasonic GA cell has recently become popular, and its nominal voltage (which also happens to be the voltage they are shipped at) is 3.6V per cell. Each GA cell has been factory-rated at 3.5-Ah. So each GA cell is (3.6 X 3.5 =) 12.6-WH.

That means you could parallel seven cells to end up with a sub-pack that is only 88.2 WH (less than 100-WH). It is only after the paralleled groups are attached to each other that the pack becomes considered dangerous by shippers, for transportation reasons. A pack made from 7P paralleled sub-packs, and using the 3.5-Ah GA cell, would have a total capacity around 24.5 Amp-Hours (Ah), which is a really huge amount of range. Most builders only want or need around 14-Ah, which can be accomplished by a relatively small 4P pack, if using the high-capacity GA cell.

Soldering the series connection on one of Micah’s battery pack kits.

In the pic above, there are three straight strings of six cells in parallel. The back row has the positive cathodes facing up, and the middle row has the negative anodes facing up. The long nickel strips have been spot-welded to connect the six-cell groups, but the connection between one six cell string and the next one can easily and safely be made with a soldering iron.

If no other sub-packs are added to the three strings “in series” shown, this would be a 3S / 6P pack. If you added more paralleled groups you can raise the voltage to your desired goal. 10S is generally regarded as 36V, and 13S is the industry standard for what is commonly called a 48V pack.

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The BMS

The Battery Management System (BMS) is an important component of any battery pack build. The one in the pic below is not from Micah’s kit, I just added this pic to show what a common BMS looks like.

A typical BMS

If you only bulk-charge a pack and it has no BMS, half of the cells will end up slightly lower than ideal, and half will likely end up with a slightly higher voltage…due to minor variances in the cells’ internal resistances. If some of the cells are overcharged, it can damage them, so a quality BMS is vital to a packs health and long life.

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What kind of soldering iron?

Doing this kit right requires a serious soldering iron. If you want to build up one of Micahs packs, I recommend a 100W soldering iron with a fat tip. A thin tip cools down too fast as soon as it touches a fat wire that is at room temperature.

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Why not just solder all of the cell ends?

So…getting back to soldering and spot-welding. It dawned on Micah that the paralleled sub-packs could be spot-welded by him. In that way, not only can they still be easily shipped to customers anywhere in the world, the end customer would only need to solder the paralleling bus-strips to each other (to form the series connections), instead of soldering onto the cell ends. If you are only connecting the paralleling bus strips to each other, and you are using a large high-wattage soldering iron, the connection will be made fast enough that the actual cell-tips will not get hot, so there is no risk of cell damage.

Micah spot-welds all the parallel connections onto the actual cell-tips, and the customer solders the series connections between the paralleled sub-packs. It’s a brilliant idea, but a new battery pack builder would also have to buy a handful of other small items from a variety of sources, and wait for each to arrive. The BMS of course, and also the wire and connectors, plus some insulating shrink wrap large enough to cover the whole pack. When buying Micah’s pack-building kit, the customer only needs to buy a cheap and high-powered soldering iron, which is something that every ebiker should own for minor repairs. We also recommend buying a digital multi-meter (DMM) for minor repairs and trouble-shooting.

Of course the easiest form of pack to build is a rectangle. But this kit allows pack-builders to also make a pack with an unusual shape, which is extremely valuable to full-suspension ebikes, because the rear shock is often located in the frame triangle, right in the middle of the best possible place to mount the weight of a battery. Hard-cases are very popular right now, such as the famous “dolphin” case. However, when squeezing a rectangle into an odd-shaped-frame, you’ll end up with a lot of wasted space. A custom pack-building kit has many more options when it comes to the shape of the pack, instead of just accepting what’s available from existing pre-built packs, out of a catalog.

If you are not familiar with Kickstarters, supporters can pre-buy a kit at a reduced price. Since the pre-buy price is significantly lower than what the retail price will be, you might be wondering what the benefit is to Micah, then. He is already making and selling these kits locally in small batches. However, when he reaches his Kickstarter goal, he will be able to purchase raw cells at a much better wholesale price.

Here is a pic of a custom-built battery pack, for a full-suspension ebike. There are many reasons someone might want to build a custom battery pack, but this reason is the one that is the most interesting to me. If you limit yourself to a slim shark pack, you would not have as much range as this custom unit.

It will also jump-start his pack-kit business, so he will have enough volume to begin adding more options when it comes to the paralleled sub-packs. He currently has a triangle-shaped 3P module, a straight 3P module (if combined they can form a triangle-shaped 6P module) and also a straight 6P module. These three current module-shapes provide a wide variety of options, and after he gets some customer feed-back, he will be able to decide which future shapes would be the most popular to add to the options list.

I’m sure this kit is not for everyone. But I also guarantee that this is a really great option for certain ebikers who would enjoy doing half of the assembly of their pack, and also want to have some control over the final shape of their pack. With this kit, Micah has done the research, and the also hardest part of the pack-build…which is assembling all the parts into one place, and spot-welding the paralleled sub-packs.

I would wish Micah luck, but…his previous enterprises have been successful, and I know that he will not need any luck for this one to be successful too.

Grew up in Los Angeles California, US Navy submarine mechanic from 1977-81/SanDiego. Hydraulic mechanic in the 1980's/Los Angeles. Heavy equipment operator in the 1990's/traveled to various locations. Dump truck driver in the 2000's/SW Utah. Currently a water plant operator since 2010/NW Kansas

4 Comments

David Morton

( October 28, 2016 )

The “discounted” prices for an ebike suitable battery are higher than finished batteries from Luncycle. Shipping maybe a bit higher. These kit prices would have to come down to be competative. Usual disclaimers.

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Thomas Jaszewski

( October 29, 2016 )

I’m not sure how you came to the price conclusion, but regardless this method means we can build custom shapes much easier, and can avoid needing a welder to prevent overheating the cells. I see more positives than problems. The only comparable packs on lunacycle are the 7Ah GA Mini. I think the kickstarter pricing is a good start. I’m in!

It was great to see support from Eric too!

Thanks Ron and Eric for supporting this great project!

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Thomas Jaszewski

( November 6, 2016 )

I just started working on a 36V pack from Micah. It’s really sweet. There aren’t a lot of choices in 36V batteries especially in stealthy shapes. I wanted a small, 10Ah, pack that would fit in a small triangle pack of a seat pack. This kit answers that need. My first one will be side by side groups. It came with 3 cells pre soldered in a triangle group. Perfect for several shapes answering my needs precisely. My uber efficient 36V will carry my nearly 20 miles with this 10Ah pack. Best of all it’s nearly unseen stuffed in a small triangle. No way could I put the materials together at a lower price, unless I bought the materials in bulk to build 10 or more batteries.